Remove coverage from python 3.8 / Django 4.2

This combination also triggers the coverage issue locally.

tox.ini

@@ -9,7 +9,7 @@ envlist =
 
 # Don't run coverage if it triggers ValueError("site must subclass AdminSite")
 # see https://github.com/nedbat/coveragepy/issues/1382
-[testenv:pypy310-5.0.x,{pypy38,pypy39,pypy310}-4.2.x]
+[testenv:pypy310-5.0.x,{pypy38,pypy39,pypy310}-4.2.x,3.8-4.2.x]
 commands =
     pip install --upgrade pip
     pip install -e .[tests]